1. Field of the Invention
The present invention relates to a battery using a battery casing made of aluminum or an aluminum alloy.
2. Description of the Related Art
For example, as shown in FIG. 3, a small-size nonaqueous electrolyte secondary battery is configured so that elements such as electric power generating elements, etc., not shown, are enclosed with a box-shaped battery casing 1 which includes a casing body portion 1a and a cover portion 1b. In the past, a nickel-plated steel plate or a stainless steel material was used in the casing body portion 1a and the cover portion 1b in the battery casing 1 of the small-size nonaqueous electrolyte secondary battery. Recently, an aluminum alloy material is often used for the purpose of reducing the weight of the battery.
For example, as shown in FIG. 4, a large-size nonaqueous electrolyte secondary battery is configured so that elements such as electric power generating elements, etc., not shown, are enclosed with an elliptic cylinder-like battery casing 1 which includes a casing body portion 1a and a cover portion 1b. In the past, a stainless steel material was also used in the casing body portion 1a and the cover portion 1b in the battery casing 1 of the large-size nonaqueous electrolyte secondary battery. Recently, an aluminum alloy material, such as a material according to JIS-A3003, is often used for the purpose of reducing the weight of the battery.
The conventional nonaqueous electrolyte secondary battery, especially a large-size one, was often used as a combination battery. Accordingly, the battery casing 1 was covered with a heat-shrinkable tube of vinyl chloride resin, a polyolefin type synthetic resin, or the like, and the tube was heated so as to shrink to thereby electrically insulate the circumference of the battery casing 1.
If the battery was wet with seawater or water when the battery casing 1 was covered with such a heat-shrinkable tube, the seawater or water penetrated into a gap between the heat-shrinkable tube and the battery casing 1 through an end portion of the heat-shrinkable tube so that the seawater or water could not go out of the gap for a long time. Further, drops of dew were often collected in the gap between the heat-shrinkable tube and the battery casing 1. Accordingly, when an aluminum alloy material was used in the battery casing 1, there was a problem of a risk of leakage of electrolytic solution because seawater or water corroded the aluminum alloy material to make a hole in the battery casing 1 if the seawater or water penetrated between the battery casing 1 if the seawater or water penetrated between the battery casing 1 and the heat-shrinkable tube. Particularly in the case of a nonaqueous electrolyte secondary battery used for marine purposes, aerospace purposes, or the like, the aforementioned problem became manifest.
It is an object of the present invention to provide a battery having a battery casing coated with synthetic resin, ceramics or alumite to thereby prevent aluminum of the battery casing from corroding.
A battery according to the present invention comprises a battery case made of aluminum or an aluminum alloy, an inside of the battery being closed with said battery casing; and a film formed on an outer surface of the battery casing, the film being one of a film of synthetic resin, a film of ceramic coating and a film formed by an aluminum oxide film-forming treatment.